Ultrasonic cleaning method



July 11, 1961 KEARNEY 2,992,142

ULTRASONIC CLEANING METHOD Filed Jan. 17, 1958 2 Sheets-Sheet 1 FIG: 1

INVENTOR. Thomas J 16262 1725,

BY full;

A TTORN E YS July 11, 1961 T. J. KEARNEY ULTRASONIC CLEANING METHOD 2 Sheets-Sheet 2 med Jan. 17, 1958 INVENTOR. T/mmas lheamzey, BY f g f e A TTORNEYS.

nited States of Michigan Filed Jan. 17, 1958, Ser. No. 709,553

Claims.

invention relates to a process of treating a work object. More particularly it is concerned with the clean ing and degreasing of intricately formed metal parts by application of chlorinated hydrocarbon solvents and ultrasonic energy. Reference is hereby made to my copending application Serial No. 438,429, filed June 22, 1954, which issued as US. Patent 2,831,785 on April 22, 1958.

Finely machined parts which have been bufied, lapsed or ground, as for example, heads for electric razors, hypodermic needles, deep drilled metal parts and the like, are very diflicult to clean and previous methods and apparatus as [ordinarily constructed did not accomplish the complete removal of grease and adhering dirt or soil from the hollows or interstices of intricately machined parts.

The generation of ultrasonic vibrations in a bath of liquid solvent has presented some difliculty. Previously compression waves have been produced from flat piezoelectric or magnetostrictive devices and standing waves have been formed. Non-uniform washing is sometimes obtained. It is thought that standing waves produced between the source of the ultrasonic energy and the surface of the liquid solvent are the cause of alternate soiled and unsoiled strips on the work object being cleaned, the distance between strips being approximately equal to one-half the wave length of the ultrasonic wave energy being used.

United States Patent No. 2,650,872 to Goldwasser discloses a method and apparatus for eliminating the alternate soiled and unsoiled strip effect. Although devices of the character illustrated in the Goldwasser patent are entirely adequate for their intended service, the present invention performs more efliciently and is less complicated, being based on a new and entirely different principle.

Accordingly, the principal object of the present invention is to provide a new and improved method for clean ing and degreasing with ultrasonic energy in a liquid solvent.

A further object of the invention is to provide a new and improved method of cleaning and deg-reasing in which the ultrasonic waves are focused. It has been found that contacting the work object with ultrasonic waves produces remarkable cleanliness. This result obtains as the focused waves strike the work object while they are converging.

Further features and objects of the invention, as well as the details of a typical and preferred embodiment thereof, will be understood from the detailed description to follow, throughout which-reference is made to the accompanying drawings wherein:

FIG. 1 represents a side elevation of a cleaning apparatus constructed in accordance with the invention.

FIG. 2 represents a view of the liquid in the well of FIG. 1 with the apparatus operating and illustrates the radially dispersed Waves of sound energy generated there- FIG. 3 represents an end view taken along line III-III of HG. 1, looking in the direction of the arrows.

FIG. 4 represents a view similar to FIG. 2, but showing a number of focused transducers of different focal length than the transducers of FIG. 2.

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Turning now to the drawings, the apparatus comprises a housing 11 which, in practice, is constructed of sheet metal. Located within the housing 11 is a well 12 which includes an overflow darn 13. Well 12 contains a chlorinated hydrocarbon liquid solvent which rises no higher in the well than the level defined by overflow dam 15 which permits the liquid to overflow into well 14. Well 12 is provided at the bottom with pipe coil 15 through which either water or steam is circulated as may be required to maintain the liquid in said well at the terriperature desired.

A pair of supporting angles 16 are fixed to the side of housing 11 and extend horizontally into the well 12 below the surface of the liquid. A transducer mounting assembly 17 supports freely a pair of transducers 18; 18a the liquid. These transducers 18, 18a are caused to vibrate at ultrasonic frequencies by any well known means. F q

A double chain conveyor 19 has a work carrier 20 depending from a cross rod 21. A work object 22 tobe cleaned is positioned on work carrier 20, and conveyor 19 operates to transport Work object 22 aroundsprocket wheels 23, 24 and 25, immersing the work object22 in the liquid of well 12. Work object 22 follows a substantially horizontal path through the liquid parallel to the liquid surface and above the transducers 18, 18a.

The transducers 18, 18a are elongate and arcuate in cross section, being formed of a section of a cylinder. Such curvilinear transducers made of barium titanate or any other electrostrictive poly-crystalline aggregate, dc} liver intense sonics energy to the focus of the transducer. From the focus the Waves disperse themselves radially over a very wide area. Ultrasonic waves are emitted the transducer 18 and are focused along a line 26 which is uniformly spaced from the base of said transducer 18. Similarly, ultrasonicwaves are emitted by the transducer 18a and are focused along a line 27 which is uniformly spaced from the base of said transducer 18a. In the specific embodiment of the invention illustrated in FIGS. l-3 of the drawings, the transducers are spaced apart from one another in a horizontal plane and the ultrasonic waves from the respective transducers intersect at a line 28 which is spaced above the focal lines 26 and 27 The conveyor 19 is arranged to carry work object 22 iii a horizontal path under the liquid surface at a level above line 28.

Referring to FIG. 4, transducers 31-35 are positioned and located in the fashion shown and emit beams 41-45 of ultrasonic waves that converge toward a line 46. Line 46 is spaced away from transducers 31-35 so that there is room for work object 22 to pass in the zone of the liquid between the line 46 and transducers 31-3 5. The beams 41-45 strike work object 22 while the beams are converging and permit cleaning at or below the focal zone. In addition to converging, each ultrasonic beam 41-45 is also focused along line 46. This arrangement has proved highly effective and has given cleaning results of the highest order. Focusing and converging the beams of ultrasonic waves subjects the work object to high intensities of ultrasonic energy, and the beams strike the work object from various angles. This is especially effective with work objects having large recesses or cavities.

According to the present invention, the work object is immersed in a bath of chlorinated hydrocarbon liquid solvent. This solvent is preferably trichlorethylene. Perchlorethylene and methylene chloride have been used and have given satisfactory results. While immersed in the bath ultrasonic waves in the range of about 200 to 1000 kilocycles are generated in the liquid which are focused and directed toward the work object, striking the work object while the ultrasonic waves are diverging as shown in FIGS. 1-3. Alternately, beams of ultrasonic waves are focused and caused to converge, and strike the work object while converging as shown in FIG. 4. The work object is transported across the ultrasonic waves in a substantially horizontal path below the surface of the liquid.

The following specific examples serve to illustrate the process of the invention:

Example I The work object is immersed in a bath of trichlorethylene at a temperature in the range of about 110 to 140 F. and subjected to ultrasonic waves of a frequency of about 400 kilocycles.

Example 2 The work object is immersed in a bath of perchlorethylene at a temperature in the range of about 140 to 170 F. and subjected to ultrasonic waves of a frequency of about 400 kilocycles.

Example 3 The work object is immersed in a bath of methylene chloride at a temperature in the range of about 58 to 78 F. and subjected to ultrasonic waves of a frequency of about 400 kilocycles.

While the specific embodiment of the invention described herein has been confined to the cleaning or degreasing of a work object by contact with a chlorinated hydrocarbon solvent, it will be appreciated that the invention can be used to accomplish a variety of objects and is not limited to cleaning or degreasing. For example, the irrvention has application in the field of plating where the work object is immersed in a liquid and the ultrasonic vibrations induce an even coating to cover the work object. Further, the work object may be predipped before being subjected tothe invention.

It is to be understood that the form of the invention herein shown and described is to be taken as a preferred embodiment. Various changes may be made in the shape, size and arrangement of parts. Equivalent elements may be substituted for those described herein, parts may be reversed, and certain features of the invention -may be utilized independently of the use of other features, all without departing from the spirit of the invention or the scope of the subjoined claim-s. For example,

the transducers can be mounted with their convex surface upward to focus the ultrasonic waves downward over a widely dispersed area. This arrangement permits passing the work object beneath the transducers Where it 4 is desired to subject the significant and diflicult upper surface, including cavities, drilled and tapped holes and the like, of a work object directly to the impact of the emitted ultrasonic longitudinal wave motion.

Having thus described my invention, I claim:

1. A method of cleaning a work object comprising the steps of immersing the work, object in a chlorinated hydrocarbon liquid, piezoelectrically creating a beam of ultrasonic waves having a frequency in the range of from 200 to 1000 kilocycles by electrically energizing piezoelectric means which is submerged in said chlorinated hydrocarbon liquid, said piezoelectric means being out of direct mechanical contact with said work object, focusing said beam of ultrasonic waves toward a focus point, and moving said work object through said liquid between said piezoelectric means and said focus point, thereby to strike said work object with said beam while said beam is converging toward the =focus point.

2. The method defined by claim 1, wherein said liquid is trichlorethylene at a temperature in the range of about to F.

3. The method defined by claim 1, wherein said liquid is perchlorethylene at a temperature in the range of about 140 to F.

4. The method defined by claim 1, wherein said liquid is methylene chloride at a temperature in the range of about 58 to 78 F.

5. A method of cleaning a work object comprising the steps of immersing the work object in a chlorinated hydrocarbon liquid, piezoeleotrically creating beams of ultrasonic waves having a frequency in the neighborhood of 400 kilocycles by electrically energizing piezoelectric means which are submerged in said chlorinated hydrocarbon liquid, said piezoelectric means being out of direct mechanical contact with said work object, causing said beams to converge by focusing each of said beams toward a focus point, and moving said work object through said liquid between said piezoelectric means and said focus point, thereby to strike said Work object with said beams while said beams are converging toward the focus point.

References Cited in the file of this patent UNITED STATES PATENTS Murdoch Sept. 30, 1958 

1. A METHOD OF CLEANING A WORK OBJECT COMPRISING THE STEPS OF IMMERSING THE WORK OBJECT IN A CHLORINATED HYDROCARBON LIQUID, PIEZOELECTRICALLY CREATING A BEAM OF ULTRASONIC WAVES HAVING A FREQUENCY IN THE RANGE OF FROM 200 TO 100 KILOCYCLES BY ELECTRICALLY ENERGIZING PIEZOELECTRIC MEANS WHICH IS SUBMERGED IN SAID CHLORINATED HYDROCARBON LIQUID, SAID PIEZOELECTRIC MEANS BEING OUT OF DIRECT MECHANICAL CONTACT WITH SAID WORK OBJECT, FOCUSING SAID BEAM OF ULTRASONIC WAVES TOWARD A FOCUS POINT, AND MOVING SAID WORK OBJECT THROUGH SAID LIQUID BETWEEN SAID PIEZOELECTRIC MEANS AND SAID FOCUS POINT, THEREBY TO STRIKE SAID WORK OBJECT WITH SAID BEAM WHILE SAID BEAM IS CONVERGING TOWARD THE FOCUS POINT. 